Glass fiber forming compositions

ABSTRACT

A glass fiber composition has 52 to 62 percent by weight SiO 2 , 0 to 2 percent by weight NaO 2 O, 16 to 25 percent by weight CaO, 8 to 16 percent by weight Al 2 O 3 , 0.05 to 0.80 percent by weight Fe 2 O 3 , 0 to 2 percent by weight K 2 , 1 to 5 percent by weight MgO, 0 to 5 percent by weight B 2 O 3 , to 0 to 2 percent by weight TiO 2 , and 0 to 1 percent by weight F, and further has a log 3 forming temperature of no greater than 1240° C. based on an NIST 714 relerence standard, a ΔT of at least 50° C., and a SiO 2 /RO ratio of no greater than 2.35.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/230474, filed Sep. 6, 2000 and PCT Application No. US00/14155, filed May 23, 2000.

[0002] The present invention relates to glass compositions for makingglass fibers, and more particular to glass compositions having loweredliquidus and forming temperatures.

[0003] The most common glass composition for making continuous glassfiber strands for textiles and glass fiber reinforcements is “E” glass.The requirements as to what type of composition constitutes an E-glasscomposition are included in ASTM D578-98. An advantage of using E-glassis that its liquidus temperature is well below its forming temperature,i.e. typically greater than 56° C. (100° F.) and generally between 83 to111° C. (150 to 200° F.). As used herein, the terms“formingtemperature”, “T_(FORM)” and “log 3 forming temperature” mean thetemperature of the glass at which the viscosity of the glass is log 3,or 1000 poise, and the terms “liquidus temperature” and “T_(LIQ)” meanthe temperature at which solid phase (crystals) and liquid phase (melt)are in equilibrium. The difference between T_(FORM) and T_(LIQ),referred to herein as “delta T” or “ΔT”, is a common measure of thecrystallization potential of a given melt composition. In the glassfiber forming industry, ΔT is typically maintained at a temperature ofat least 50° C. (90° F.) in order to prevent devitrification of themolten glass during a glass fiber forming operation, and in particularin the bushing area.

[0004] Boron and fluorine containing glass were developed to meet theseoperating conditions. More specifically, the boron and fluorine wereincluded in the glass batch materials to act as fluxes during the glassmelting operation. In particular, E-glass can include up to 10 wt % B₂O₃and up to 1.0 fluoride (see ASTM D 578-00 §4.2). However, thesematerials are volatilized during melting and boron and fluorineemissions are released to the atmosphere. Since boron and fluorine areconsidered pollutants, these emissions are closely controlled byenvironmental regulations, which in turn requires careful control of thefurnace operations and the use of expensive pollution control equipment.In response to this, low boron and/or low fluorine E-glasses weredeveloped. As used herein, “low boron” means that the glass compositionis no greater than 5 weight percent (wt %) boron, and includesboron-free glass, and “low fluorine” means that the glass composition isno greater than 0.30 wt % fluorine, and includes fluorine-free glass.

[0005] For additional information concerning glass compositions andmethods for fiberizing the glass composition, see K. Loewenstein, TheManufacturing Technology of Continuous Glass Fibres, (3d Ed. 1993) atpages 30-44, 47-60, 115-122 and 126-135, and F. T. Wallenberger(editor), Advanced Inorganic Fibers: Processes, Structures, Properties,Applications, (2000) at pages 81-102 and 129-168, which are herebyincorporated by reference.

[0006] Because the actual glass fiber forming operation is conducted athigh temperatures, there is high energy usage associated with itsproduction, along with associated high energy costs. In addition, thehigh temperatures accelerate the degradation of the refractory used inthe glass melting furnace, as well as the bushings used to form thefibers. The bushings include precious metals that cannot be recoveredfrom the glass as the bushings corrode. It would be advantageous toproduce the glass fibers at the lowest possible forming and liquidustemperatures so as to reduce the energy usage and costs and thermal loadon the furnace refractory and bushings, while at the same time providethe ΔT required to ensure an uninterrupted glass fiber formingoperation. Reducing the forming and liquidus temperatures of the glasscompositions can also result in environmental benefits, such as but notlimited to, a reduction in the amount of fuel required to generate theenergy necessary for the fiber forming operation, as well as a reductionin the flue gas temperature. In addition, it would be advantageous ifthe glass compositions are low fluorine and/or low boron compositions soas to reduce or eliminate the environmental pollutants associated withthese materials.

[0007] The present invention provides a low boron content glass fiberforming composition that has a forming temperature of no greater than1240° C. (2262° F.), a ΔT of at least 50° C. (90° F.), and a ratio ofSiO₂ to RO (i.e. CaO+MgO) of no greater than 2.35. In one nonlimitingembodiment of the present invention, the glass composition has a silicacontent of no greater than 59 weight percent. In another nonlimitingembodiment of the invention, the glass composition is boron-free.

[0008] The foregoing summary, as well as the following detaileddescription of embodiments of the present invention, will be betterunderstood when read in conjunction with the appended drawings. In thedrawings:

[0009] FIGS. 1-6 are curves showing the relationship between the ratioof SiO₂ to RO of various glass fiber forming compositions to thecompositions' forming and liquidus temperatures based on the data shownin corresponding Tables A through F, respectively.

[0010] The base composition for the low boron glass fibers of thepresent invention suitable for textiles and glass fiber reinforcementsincludes the following main constituents in weight percent based on thetotal weight of the final glass composition. broad alternate range rangeSiO₂ (wt %)   52 to 62 53 to 59 Na₂O (wt %)   0 to 2 up to 1.5 CaO (wt%)   16 to 25 20 to 25 Al₂O₃ (wt %)   8 to 16 11 to 14 Fe₂O₃ (wt %) 0.05to 0.80 up to 0.5 K₂O (wt %)   0 to 2 up to 1

[0011] It should be appreciated that, unless otherwise indicated, allnumerical values discussed herein, such as but not limited to weightpercent of materials or temperatures, are approximate and are subject tovariations due to various factors well known to those skilled in the artsuch as, but not limited to, measurement standards, equipment andtechniques. As a result, such values are to be understood as beingmodified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties sought to be obtained by thepresent invention. At the very least each numerical parameter should atleast be construed in light of the number of reported significant digitsand by applying ordinary rounding techniques. For example, where itstates in the present application that the range for SiO₂ is 52 to 62weight percent, this range is about 52 to about 62 weight percent, andwhere it states that the forming temperature of a glass compositionshould be no greater than 1249° C. (2280° F.), the temperature is about1249° C.

[0012] Notwithstanding that the numerical ranges and parameters settingforth the broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

[0013] In addition, where the amount of a particular material orcombinations of materials disclosed herein is expressed in terms of“percent” or “%”, it should be understood that this means “weightpercent” or “wt %”.

[0014] Additional materials can be added to the glass composition tomodify the melt properties of the glass. For example, and withoutlimiting the glass compositions disclosed herein, Li₂O, ZnO, MnO and/orMnO₂, can be added to the glass fiber composition to reduce T_(FORM)and/or T_(LIQ). In one non-limiting embodiment of the present invention,the glass composition includes 0 to 1.5 wt % Li₂O and/or 0 to 1.5 wt %ZnO and/or 0 to 3 wt % MnO and/or 0 to 3 wt % MnO₂. It is believed thatlevels of these materials less than 0.05 wt % would be considered eithertramp amounts or so low that they will not materially impact the glassmelt properties. As a result, in another non-limiting embodiment, 0.05to 1.5 wt % Li₂O and/or 0.05 to 1.5 wt % ZnO and/or 0.05 to 3 wt % MnOand/or 0.05 to 3 wt % MnO₂ are included in the glass composition. Instill another nonlimiting embodiment of the invention, the glasscompositions include 0.2 to 1 wt % Li₂O and/or 0.2 to 1 wt % ZnO and/orup to 1 wt % MnO and/or up to 1 wt % MnO₂.

[0015] MgO is another material typically included in a glass fiberforming composition. It has been found that the heating and meltingprofile of a glass fiber composition, and in particular the liquidustemperature, can be controlled and in particular optimized bycontrolling the amount of MgO. In addition, it has been determined thata eutectic (minimum liquidus temperature) exists in a generic quaternarySiO₂—Al₂O₃—CaO—MgO at around 2.5 wt % MgO (see PCT Application No. US00/14155, which is incorporated herein by reference). Without limitingthe present invention, in one nonlimiting embodiment, the glass fibercomposition includes 1 to 5 wt % MgO, e.g. 1 to 4 wt % or 1.7 to 2.9 wt% or 1.9 to 2.65 wt % MgO.

[0016] Boron is another material that can be added to glass fibercompositions to reduce T_(FORM) and T_(LIQ). However, as discussedearlier, the inclusion of boron results in the production of particulateemissions that, depending on the particulate level, may have to beremoved from a melting furnace exhaust stream before being released intothe environment. Although the amount of B₂O₃ in a glass fibercomposition can be as high as 10 wt %, in the present invention, theglass composition has a low boron content, i.e. has a B₂O₃ content of nogreater than 5 wt %. In other nonlimiting embodiments of the presentinvention, the glass fiber composition has no greater than 4 wt %, or nogreater than 3 wt %, or no greater than 2 wt % B₂O₃. In anothernonlimiting embodiment of a glass fiber forming composition, the lowboron content glass composition is essentially boron-free, i.e. itincludes no more than a trace amount of B₂O₃, which is considered hereinto be up to 0.05 wt % B₂O₃. In still another nonlimiting embodiment, thelow boron content glass fiber composition does not include any B₂O₃.

[0017] It should be appreciated that glass fiber compositions caninclude other constituents and the present invention contemplates theinclusion of other materials in the glass fiber compositions, such as,but not limited to, 0 to 2 wt % each of TiO₂, BaO, ZrO₂ and SrO, e.g. upto 1.5 wt % or up to 1 wt % of each of these materials.

[0018] In addition, because of the environmental concerns discussedearlier, in one nonlimiting embodiment of the present invention, theglass composition has a low fluorine content. In another nonlimitingembodiment, the glass composition is fluorine-free, i.e. it includes nomore than a trace amount of fluorine, which is considered herein to beup to 0.05 wt % fluorine. In still another nonlimiting embodiment, theglass composition does not include any fluorine. Except where otherwiseindicated, the glass fiber forming compositions disclosed and discussedherein are fluorine-free.

[0019] It should be appreciated that the glass compositions disclosedherein can also include small amounts of other materials, for examplemelting and refining aids, tramp materials or impurities. For exampleand without limiting the present invention, melting and fining aids,such as SO₃, are useful during production of the glass, but theirresidual amounts in the glass can vary and have minimal, if any,material effect on the properties of the glass product. In addition,small amounts of the additives discussed above can enter the glasscomposition as tramp materials or impurities included in the rawmaterials of the main constituents.

[0020] Commercial glass fibers of the present invention can be preparedin the conventional manner well known in the art, by blending the rawmaterials used to supply the specific oxides that form the compositionof the fibers. For example, typically sand is used for SiO₂, clay forAl₂O₃, lime or limestone for CaO, and dolomite for MgO and some of theCaO. As discussed earlier, the glass can include other additives thatare added to modify the glass properties as well as small amounts ofmelting and refining aids, tramp materials or impurities.

[0021] After the ingredients are mixed in the proper proportions toprovide the desired weight of each constituent for the desired glass,the batch is melted in a conventional glass fiber melting furnace andthe resulting molten glass is passed along a conventional forehearth andinto a glass fiber forming bushing located along the bottom of theforehearth, as is well known to those skilled in the art. During theglass melting phase, the glass batch materials are typically heated to atemperature of at least 1400° C. (2550° F.). The molten glass is thendrawn or pulled through a plurality of holes in the bottom of thebushing. The streams of molten glass are attenuated to form filaments bygathering a plurality of filaments together to form a strand and windingthe strand on a forming tube mounted on a rotatable collet of a windingmachine. Alternatively, the fiber forming apparatus can be, for example,a forming device for synthetic textile fibers or strands in which fibersare drawn from nozzles, for example a spinneret, wherein fibers aredrawn through holes in a plate, as is known to those skilled in the art.Typical forehearths and glass fiber forming arrangements are shown in K.Loewenstein, The Manufacturing Technology of Continuous Glass Fibres,(Third Edition 1993) at pages 85-107 and pages 115-135, which are herebyincorporated by reference.

[0022] Several series of different types of low boron glass fibercompositions were made to examine certain relationships between theamount of selected glass constituents and the corresponding forming andliquidus temperatures in order to identify glass compositions having alowered forming temperature and a desired ΔT. During testing, the glasscompositions for the different series of experimental samples weredivided into the following main compositional categories andsubcategories:

[0023] Type I—high T_(FORM) (T_(FORM)>1240° C.), low boron content

[0024] Type I-1 boron-free

[0025] Type I-2 up to 2.5 wt % B₂O₃

[0026] Type II—low T_(FORM) (T_(FORM)≦1240° C.), low boron content, 2.5wt % MgO

[0027] Type II-1 boron-free

[0028] Type II-2 up to 5 wt % B₂O₃

[0029] Type III—low T_(FORM) (T_(FORM)≦1240° C.), low boron content, 2.5wt % MgO, lithium and/or zinc

[0030] Type III-1 boron-free with lithium

[0031] Type III-2 boron-free with lithium and zinc

[0032] Type III-3 boron-free with zinc

[0033] Type III-4 up to 5 wt % B₂O₃ with lithium

[0034] Type I-1 glasses would include prior art glasses such as thosedisclosed in Example 1 of French Patent 2,768,144 (hereinafter “Patent'144”), U.S. Pat. Nos. 4,542,106 and 5,789,329 (hereinafter “Patent'106” and “Patent '329”, respectively), and ADVANTEX® glass, which iscommercially available from Owens Corning Fiberglass, and typicallyinclude approximately 60 wt % SiO₂, 25 wt % CaO+MgO (hereinafter “RO”),and 12-14 wt % Al₂O₃ and are boron-free. Type I-2 glasses would includeprior art glasses such as that disclosed in Example 2 Patent '144, whichincludes 1.8 wt % B₂O₃ and 60.82 wt % SiO₂.

[0035] Tables A through F include examples of each series of glass fibercompositions and were used to generate corresponding FIGS. 1-6,respectively, as will be discussed late in more detail. In Table A,Examples 1-8 are Type II-1 glasses while Examples 9-34 are Type I-1glasses. In Table B, Examples 35-77 are Type II-2 glasses while Examples78-83 are Type I-2 glasses. In Table C, Examples 84-143 and 152-156 areType III-1 glasses while Examples 144-151 are similar but have a log 3forming temperature greater than 1240° C. In Table D, Examples 157-171are Type III-2 glasses while Examples 172-183 are similar but have a log3 forming temperature greater than 1240° C. In Table E, Examples 194-197are Type III-3 glasses while Examples 184-193 are similar but have a log3 forming temperature greater than 1240° C. In Table F, Examples 198-296are Type III-4 glasses while Examples 297 and 298 are similar but have alog 3 forming temperature greater than 1240° C. TABLE A TYPE I-1 ANDII-1 GLASS Composition Examples Weight % 1 2 3 4 5 6 7 8 9 10 SiO2 57.9557.75 58.05 57.65 57.45 58.72 57.72 59.05 60.13 60.63 Al2O3 13.20 13.2013.40 13.40 13.40 11.65 11.64 12.20 12.27 12.27 CaO 24.05 24.25 23.7524.15 24.35 24.58 25.58 23.95 22.92 22.42 MgO 2.55 2.55 2.55 2.55 2.552.61 2.61 2.55 2.50 2.50 TiO2 1.10 1.10 1.10 1.10 1.10 1.12 1.12 1.101.00 1.00 Na2O 0.90 0.90 0.90 0.90 0.90 0.92 0.92 0.90 0.98 K2O 0.050.05 Fe2O3 0.25 0.25 0.25 0.25 0.25 0.27 0.27 0.25 0.20 0.20 SO3 0.020.02 SiO2/RO 2.18 2.15 2.21 2.16 2.13 2.16 2.05 2.23 2.37 2.43 T_(FORM)(° C.) 1235 1232 1240 1240 1238 1230 1222 1239 1265 1268 T_(LIQ) (° C.)1164 1166 1167 1166 1165 1198 1215 1181 1164 1166 ΔT (° C.) 71 66 73 7474 32 7 58 101 102 Composition Examples Weight % 11 12 13 14 15 16 17 1819 20 SiO2 60.13 59.61 59.45 59.40 59.35 59.30 59.25 59.10 59.00 58.85Al2O3 12.27 12.16 12.20 12.20 12.20 12.20 12.20 12.20 12.20 12.20 CaO22.92 23.51 23.55 23.60 23.65 23.70 23.75 23.90 24.00 24.15 MgO 2.502.62 2.55 2.55 2.55 2.55 2.55 2.55 2.55 2.55 TiO2 1.00 1.00 1.10 1.101.10 1.10 1.10 1.10 1.10 1.10 Na2O 0.98 0.90 0.90 0.90 0.90 0.90 0.900.90 0.90 0.90 K2O Fe2O3 0.20 0.20 0.25 0.25 0.25 0.25 0.25 0.25 0.250.25 SO3 SiO2/RO 2.37 2.28 2.28 2.27 2.27 2.26 2.25 2.23 2.22 2.20T_(FORM) (° C.) 1262 1251 1258 1250 1242 1248 1249 1247 1245 1242T_(LIQ) (° C.) 1164 1170 1173 1178 1176 1180 1178 1178 1178 1186 ΔT (°C.) 98 81 85 72 66 68 71 69 67 56 Composition Examples Weight % 21 22 2324 25 26 27 28 29 30 SiO2 59.25 59.15 58.35 58.15 58.25 57.85 57.6558.15 57.95 57.75 Al2O3 12.40 12.60 13.20 13.20 13.40 13.40 13.40 13.2013.20 13.20 CaO 23.55 23.45 23.65 23.85 23.55 23.95 24.15 23.85 24.0524.25 MgO 2.55 2.55 2.55 2.55 2.55 2.55 2.55 2.55 2.55 2.55 TiO2 1.101.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 Na2O 0.90 0.90 0.90 0.900.90 0.90 0.90 0.90 0.90 0.90 K2O Fe2O3 0.25 0.25 0.25 0.25 0.25 0.250.25 0.25 0.25 0.25 SO3 SiO2/RO 2.27 2.28 2.23 2.20 2.23 2.18 2.16 2.202.18 2.15 T_(FORM) (° C.) 1253 1253 1248 1245 1244 1243 1242 1249 12461243 T_(LIQ) (° C.) 1171 1168 1162 1160 1174 1174 1169 1170 1171 1172 ΔT(° C.) 82 85 86 85 70 69 73 79 75 71 Composition Examples Weight % 31 3233 34 SiO2 57.55 58.05 58.85 59.61 Al2O3 13.20 13.40 13.40 12.16 CaO24.45 23.75 23.95 23.51 MgO 2.55 2.55 2.55 2.62 TiO2 1.10 1.10 1.10 1.00Na2O 0.90 0.90 0.90 0.90 K2O Fe2O3 0.25 0.25 0.25 0.20 SO3 SiO2/RO 2.132.21 2.22 2.28 T_(FORM) (° C.) 1241 1246 1248 1251 T_(LIQ) (° C.) 11641163 1171 1167 ΔT (° C.) 67 83 77 84

[0036] TABLE B TYPE I-2 AND II-2 GLASS Composition Examples Weight % 3536 37 38 39 40 41 42 43 44 SiO2 57.75 57.75 56.75 57.15 57.25 58.5555.40 55.80 56.20 55.75 Al2O3 13.20 12.20 13.20 13.05 13.20 12.20 13.6013.40 13.60 13.20 CaO 24.25 24.25 24.25 24.00 24.25 23.45 24.85 24.6524.05 23.25 MgO 2.50 2.50 2.50 2.55 2.50 2.55 2.50 2.50 2.50 2.55 TiO21.10 1.10 1.10 1.10 1.10 1.10 0.50 0.50 0.50 1.10 Na2O 0.90 0.90 0.900.90 0.90 0.90 0.90 0.90 0.90 0.90 Fe2O3 0.25 0.25 0.25 0.25 0.25 0.250.25 0.25 0.25 0.25 B2O3 1.00 1.00 1.00 1.00 1.00 1.00 2.00 2.00 2.003.00 SiO2/RO 2.16 2.16 2.12 2.15 2.14 2.25 2.03 2.06 2.12 2.16 T_(FORM)(° C.) 1240 1227 1228 1235 1239 1236 1217 1211 1219 1204 T_(LIQ) (° C.)1178 1164 1161 1154 1159 1159 1153 1156 1136 1127 ΔT (° C.) 62 63 67 8180 77 64 55 83 77 Composition Examples Weight % 45 46 47 48 49 50 51 5253 54 SiO2 57.25 56.25 56.65 56.75 58.05 56.35 56.40 56.45 55.60 55.80Al2O3 12.20 13.20 13.05 13.20 12.20 13.60 13.60 13.55 13.60 13.60 CaO23.75 23.75 23.50 23.25 22.95 23.85 23.80 23.80 24.65 24.45 MgO 2.502.50 2.55 2.55 2.55 2.55 2.55 2.55 2.50 2.50 TiO2 1.10 1.10 1.10 1.101.10 0.50 0.50 0.50 0.50 0.50 Na2O 0.90 0.90 0.90 0.90 0.90 0.90 0.900.90 0.90 0.90 Fe2O3 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25B2O3 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 SiO2/RO 2.18 2.142.17 2.20 2.28 2.13 2.14 2.14 2.05 2.07 T_(FORM) (° C.) 1227 1224 12251225 1225 1218 1219 1220 1211 1209 T_(LIQ) (° C.) 1148 1149 1145 11471142 1138 1142 1137 1154 1156 ΔT (° C.) 79 75 80 78 83 80 77 83 57 53Composition Examples Weight % 55 56 57 58 59 60 61 62 63 64 SiO2 56.5056.60 56.40 56.0 56.40 56.20 56.00 56.00 55.80 56.50 Al2O3 13.55 13.4013.40 13.60 13.60 13.80 13.80 13.60 13.60 13.20 CaO 23.85 23.85 24.0524.25 23.85 23.85 24.05 24.25 24.45 23.50 MgO 2.55 2.50 2.50 2.50 2.502.50 2.50 2.50 2.50 2.55 TiO2 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.500.50 1.10 Na2O 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 Fe2O30.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 B2O3 2.00 2.00 2.002.00 2.00 2.00 2.00 2.00 2.00 2.00 SiO2/RO 2.14 2.15 2.12 2.09 2.14 2.132.11 2.09 2.07 2.16 T_(FORM) (° C.) 1217 1222 1216 1213 1220 1223 12191202 1222 1220 T_(LIQ) (° C.) 1135 1139 1143 1136 1139 1158 1151 11371153 1133 ΔT (° C.) 82 83 73 77 81 65 68 65 69 87 Composition ExamplesWeight % 65 66 67 68 69 70 71 72 73 74 SiO2 57.25 56.75 56.25 56.7556.65 56.80 56.40 55.80 55.60 55.00 Al2O3 13.20 13.20 13.20 13.45 13.0513.40 13.80 13.80 13.40 13.80 CaO 22.75 23.75 23.75 23.00 23.50 23.6523.65 24.25 24.85 25.05 MgO 2.50 2.05 2.55 2.55 2.55 2.50 2.50 2.50 2.502.50 TiO2 1.10 1.10 1.10 1.10 1.10 0.50 0.50 0.50 0.50 0.50 Na2O 0.900.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 Fe2O3 0.25 0.25 0.25 0.250.25 0.25 0.25 0.25 0.25 0.25 B2O3 2.00 2.00 2.00 2.00 2.00 2.00 2.002.00 2.00 2.00 SiO2/RO 2.27 2.20 2.14 2.22 2.17 2.17 2.16 2.09 2.03 2.00T_(FORM) (° C.) 1237 1230 1220 1227 1218 1228 1197 1222 1209 1206T_(LIQ) (° C.) 1149 1141 1131 1131 1113 1141 1156 1137 1168 1169 ΔT (°C.) 86 89 89 96 87 87 41 85 41 47 Composition Examples Weight % 75 76 7778 79 80 81 82 83 SiO2 56.75 56.15 56.25 58.61 59.01 58.70 57.75 59.0559.11 Al2O3 13.20 13.05 13.20 12.16 12.04 13.35 13.20 12.20 12.16 CaO22.25 23.00 23.25 23.50 23.27 23.50 23.25 23.95 23.00 MgO 2.55 2.55 2.552.50 2.48 2.50 2.50 2.55 2.50 TiO2 1.10 1.10 1.10 1.10 1.09 0.50 1.101.10 1.10 Na2O 0.90 0.90 0.90 0.90 0.89 0.30 0.90 0.90 0.90 Fe2O3 0.250.25 0.25 0.23 0.23 0.25 0.25 0.25 0.23 B2O3 3.00 3.00 3.00 1.00 1.000.90 1.00 1.00 1.00 SiO2/RO 2.29 2.20 2.18 2.25 2.29 2.26 2.24 2.23 2.32T_(FORM) (° C.) 1221 1212 1214 1242 1252 1253 1250 1254 1248 T_(LIQ) (°C.) 1121 1178 1114 1161 1178 1145 1154 1183 1152 ΔT (° C.) 100 34 100 8174 108 96 71 96

[0037] TABLE C TYPE III-1 GLASS Composition Examples Weight % 84 85 8687 88 89 90 91 92 93 SiO2 58.70 58.70 58.35 58.25 58.86 58.76 57.9557.65 58.96 58.15 Al2O3 13.35 13.35 13.20 13.40 13.44 13.64 13.20 13.4013.24 13.20 CaO 23.50 23.50 23.65 23.55 23.55 23.45 24.05 24.15 23.6523.85 MgO 2.50 2.50 2.55 2.55 2.50 2.50 2.55 2.55 2.50 2.55 TiO2 0.500.50 1.10 1.10 0.50 0.50 1.10 1.10 0.50 1.10 Na2O 0.60 0.30 Li2O 0.600.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 Fe2O3 0.25 0.25 0.25 0.250.25 0.25 0.25 0.25 0.25 0.25 SiO2/RO 2.26 2.26 2.23 2.23 2.26 2.26 2.182.16 2.25 2.20 T_(FORM) (° C.) 1226 1211 1211 1215 1216 1218 1205 12061212 1237 T_(LIQ) (° C.) 1157 1153 1146 1153 1153 1150 1151 1154 11581172 ΔT (° C.) 69 58 65 62 63 68 54 52 54 65 Composition Examples Weight% 94 95 96 97 98 99 100 101 102 103 SiO2 59.61 59.97 60.09 60.21 60.3359.61 59.61 59.73 59.85 59.97 Al2O3 12.12 12.19 12.22 12.24 12.27 12.9212.92 12.92 12.95 12.97 CaO 22.12 23.56 23.31 23.35 23.40 21.91 21.9622.00 22.04 22.09 MgO 3.50 2.90 2.70 2.50 2.30 3.50 3.30 3.10 2.90 2.70TiO2 0.50 0.50 0.50 0.50 0.50 1.10 1.10 1.10 1.10 1.10 Na2O Li2O 0.900.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 Fe2O3 0.25 0.25 0.25 0.250.25 0.25 0.25 0.25 0.25 0.25 SiO2/RO 2.33 2.27 2.31 2.33 2.35 2.35 2.362.38 2.40 2.42 T_(FORM) (° C.) 1205 1207 1217 1213 1216 1213 1213 12141214 1219 T_(LIQ) (° C.) 1190 1170 1163 1162 1166 1179 1170 1164 11611160 ΔT (° C.) 15 37 54 51 50 34 43 50 53 59 Composition Examples Weight% 104 105 106 107 108 109 110 111 112 113 SiO2 60.09 60.21 60.00 60.5759.80 59.75 59.65 59.60 59.55 59.50 Al2O3 13.00 13.02 12.50 13.10 12.2512.25 12.25 12.25 12.25 12.25 CaO 22.13 22.18 23.70 22.31 22.60 22.8523.35 23.60 23.85 24.10 MgO 2.50 2.30 1.90 1.70 3.10 2.90 2.50 2.30 2.101.90 TiO2 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 Na2O 0.300.30 0.30 0.30 0.30 0.30 Li2O 0.90 0.90 0.90 0.90 0.60 0.60 0.60 0.600.60 0.60 Fe2O3 0.25 0.25 0.25 0.25 SiO2/RO 2.44 2.46 2.34 2.52 2.332.32 2.31 2.30 2.29 2.29 T_(FORM) (° C.) 1223 1233 1239 1239 1240 12361236 1238 1234 1234 T_(LIQ) (° C.) 1155 1142 1139 1141 1156 1156 11591167 1173 1181 ΔT (° C.) 68 91 100 98 94 80 77 71 61 53 CompositionExamples Weight % 114 115 116 117 118 119 120 121 122 123 SiO2 59.4560.00 59.95 59.90 59.85 59.61 59.97 60.09 60.21 60.33 Al2O3 12.25 12.4012.40 12.40 12.0 12.12 12.19 12.22 12.24 12.27 CaO 24.35 22.05 23.3023.55 23.80 22.12 22.25 22.30 22.34 22.39 MgO 1.70 2.30 2.10 1.90 1.703.50 2.90 2.70 2.50 2.30 TiO2 1.10 1.10 1.10 1.10 1.10 1.50 1.50 1.501.50 1.50 Na2O 0.30 Li2O 0.60 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.900.90 Fe2O3 0.25 0.25 0.26 0.25 0.25 0.25 0.25 0.25 0.25 SiO2/RO 2.282.46 2.36 2.35 2.35 2.33 2.38 2.40 2.42 2.44 T_(FORM) (° C.) 1234 12301231 1224 1224 1215 1217 1213 1215 1231 T_(LIQ) (° C.) 1192 1146 11521156 1156 1181 1161 1178 1162 1160 ΔT (° C.) 42 84 79 68 68 34 56 35 5371 Composition Examples Weight % 124 125 126 127 128 129 130 131 132 133SiO2 60.75 60.21 59.78 58.70 57.75 58.05 57.85 59.71 59.46 60.02 Al2O312.35 13.02 12.30 13.35 13.20 13.40 13.40 13.24 13.24 12.35 CaO 22.5522.52 23.26 23.50 24.25 23.75 23.95 22.90 23.15 23.35 MgO 1.70 2.50 2.532.50 2.55 2.55 2.55 2.50 2.50 2.54 TiO2 1.50 0.50 0.50 0.50 1.10 1.101.10 0.50 0.50 0.50 Na2O 0.00 Li2O 0.90 1.00 1.40 1.20 0.90 0.90 0.900.90 0.90 1.00 Fe2O3 0.25 0.25 0.23 0.25 0.25 0.25 0.25 0.25 0.25 0.23SiO2/RO 2.51 2.41 2.32 2.26 2.15 2.21 2.18 2.35 2.32 2.32 T_(FORM) (°C.) 1240 1231 1187 1194 1201 1202 1199 1227 1226 1209 T_(LIQ) (° C.)1166 1143 1158 1149 1155 1153 1157 1142 1147 1159 ΔT (° C.) 74 88 29 4546 49 42 85 79 50 Composition Examples Weight % 134 135 136 137 138 139140 141 142 143 SiO2 59.90 60.26 60.14 59.16 60.10 60.23 60.10 60.2359.78 60.14 Al2O3 12.32 12.40 12.37 13.24 13.00 12.25 13.00 12.25 12.3012.37 CaO 23.31 23.45 23.40 23.45 22.15 23.36 22.15 23.36 23.26 23.40MgO 2.53 2.55 2.54 2.50 2.50 2.50 2.50 2.50 2.53 2.54 TiO2 0.50 0.510.51 0.50 1.10 0.51 1.10 0.51 0.50 0.51 Na2O Li2O 1.20 0.60 0.80 0.900.90 0.90 0.90 0.90 1.40 0.80 Fe2O3 0.23 0.23 0.23 0.25 0.25 0.25 0.250.25 0.23 0.23 SiO2/RO 2.32 2.32 2.32 2.28 2.44 2.33 2.44 2.33 2.32 2.32T_(FORM) (° C.) 1199 1230 1219 1218 1235 1220 1237 1224 1198 1219T_(LIQ) (° C.) 1160 1158 1159 1156 1133 1160 1136 1158 1156 1159 ΔT (°C.) 39 72 60 62 102 60 101 66 42 60 Composition Examples Weight % 144145 146 147 148 149 150 151 SiO2 60.38 60.33 59.70 60.21 60.21 60.2160.50 58.70 Al2O3 12.42 13.05 12.25 13.02 13.02 13.02 12.45 13.35 CaO23.50 22.22 22.85 22.52 22.52 22.52 23.54 23.50 MgO 2.55 2.10 2.70 2.502.50 2.50 2.56 2.50 TiO2 0.51 1.10 1.10 0.50 0.50 0.50 0.51 0.50 Na2O0.30 0.25 0.50 0.75 0.90 Li2O 0.40 0.90 0.60 0.75 0.50 0.25 0.20 0.30Fe2O3 0.23 0.25 0.25 0.25 0.25 0.24 0.25 SiO2/RO 2.32 2.48 2.34 2.412.41 2.41 2.32 2.26 T_(FORM) (° C.) 1244 1258 1242 1242 1253 1263 12561241 T_(LIQ) (° C.) 1158 1136 1155 1147 1152 1160 1158 1165 ΔT (° C.) 86122 87 95 101 103 98 76 Composition Examples Weight % 152 153 154 155156* SiO2 60.05 60.05 60.05 59.30 59.30 Al2O3 12.98 12.98 12.98 12.1012.10 CaO 22.14 22.14 22.14 22.60 22.60 MgO 3.12 3.12 3.12 3.40 3.40TiO2 0.55 0.55 0.55 1.50 1.50 Na2O 0.45 Li2O 0.91 0.91 0.91 0.45 0.90Fe2O3 0.25 0.25 0.25 0.20 0.20 SiO2/RO 2.38 2.38 2.38 2.28 2.28 T_(FORM)(° C.) 1214 1219 1223 1218 1191 (NIST 710A) T_(LIQ) (° C.) 1159 11641163 1179 1187 ΔT (° C.) 55 55 60 39 4

[0038] TABLE D TYPE III-2 GLASS Composition Examples Weight % 157 158159 160 161 162 163 164 165 166 SiO2 58.25 58.30 58.20 58.10 58.00 58.1558.15 58.10 57.35 57.95 Al2O3 13.33 13.03 13.03 13.03 13.03 13.20 13.3313.63 13.20 13.20 CaO 23.29 23.54 23.64 23.74 23.84 22.85 23.39 23.1423.65 24.05 MgO 2.50 2.50 2.50 2.50 2.50 2.55 2.50 2.50 2.55 2.55 TiO20.50 0.50 0.50 0.50 0.50 1.10 0.50 0.50 1.10 1.10 Na2O Li2O 0.90 0.900.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 ZnO 1.00 1.00 1.00 1.00 1.001.00 1.00 1.00 1.00 1.00 Fe2O3 0.23 0.23 0.23 0.23 0.23 0.25 0.23 0.230.25 0.25 SiO2/RO 2.26 2.24 2.23 2.21 2.20 2.29 2.25 2.26 2.19 2.18T_(FORM) (° C.) 1213 1204 1205 1206 1208 1207 1208 1212 1195 1195T_(LIQ) (° C.) 1146 1147 1148 1144 1149 1136 1152 1157 1141 1140 ΔT (°C.) 67 57 57 62 59 71 56 55 54 55 Composition Examples Weight % 167 168169 170 171 172 173 174 175 176 SiO2 59.61 59.47 59.12 57.75 58.00 59.7359.85 59.97 60.09 60.21 Al2O3 12.16 12.16 12.00 13.20 13.63 12.92 12.9512.97 13.00 13.02 CaO 23.50 24.22 22.50 24.25 23.24 22.00 22.04 22.0922.13 22.18 MgO 2.50 1.90 3.40 2.55 2.50 3.10 2.90 2.70 2.50 2.30 TiO21.10 1.10 1.00 1.10 0.50 1.10 1.10 1.10 1.10 1.10 Na2O Li2O 0.45 0.450.90 0.90 0.90 0.45 0.45 0.45 0.45 0.45 ZnO 0.45 0.45 1.00 1.00 1.000.45 0.45 0.45 0.45 0.45 Fe2O3 0.20 0.25 0.23 0.25 0.25 0.25 0.25 0.25SiO2/RO 2.29 2.28 2.28 2.15 2.25 2.38 2.40 2.42 2.44 2.46 T_(FORM) (°C.) 1229 1218 1190 1194 1212 1242 1246 1246 1251 1251 T_(LIQ) (° C.)1154 1159 1163 1159 1163 1173 1168 1154 1147 1144 ΔT (° C.) 75 59 27 3549 69 78 92 104 107 Composition Examples Weight % 177 178 179 180 181182 183 SiO2 60.33 60.45 60.57 59.40 59.20 59.54 59.40 Al2O3 13.05 13.0813.10 12.16 12.16 12.16 12.16 CaO 22.22 22.27 22.31 23.49 23.69 23.9524.49 MgO 2.10 1.90 1.70 2.30 2.30 2.10 1.70 TiO2 1.10 1.10 1.10 1.101.10 1.10 1.10 Na2O 0.40 0.40 Li2O 0.45 0.45 0.45 0.45 0.45 0.45 0.45ZnO 0.45 0.45 0.45 0.45 0.45 0.45 0.45 Fe2O3 0.25 0.25 0.25 SiO2/RO 2.482.50 2.52 2.30 2.28 2.29 2.27 T_(FORM) (° C.) 1260 1260 1263 1245 12471241 1245 T_(LIQ) (° C.) 1140 1139 1135 1159 1152 1155 1168 ΔT (° C.)120 121 128 86 95 86 77

[0039] TABLE E TYPE III-3 GLASS Composition Examples Weight % 184 185186 187 188 189 190 191 192 193 SiO2 59.73 59.85 59.97 60.09 60.21 60.3360.45 60.57 58.80 58.70 Al2O3 12.92 12.95 12.97 13.00 13.02 13.05 13.0813.10 13.00 11.90 CaO 22.00 22.04 22.09 22.13 22.18 22.22 22.27 22.3123.45 22.40 MgO 3.10 2.90 2.70 2.50 2.30 2.10 1.90 1.70 2.50 3.40 TiO21.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.50 ZnO 0.90 0.90 0.900.90 0.90 0.90 0.90 0.90 0.90 1.00 Na2O 0.90 K2O Fe2O3 0.25 0.25 0.250.25 0.25 0.25 0.25 0.25 0.25 0.20 SiO2/RO 2.38 2.40 2.42 2.44 2.46 2.482.50 2.52 2.27 2.28 T_(FORM) (° C.) 1265 1267 1273 1278 1273 1280 12851275 1268 1226 T_(LIQ) (° C.) 1170 1166 1159 1157 1166 1169 1170 11711165 1180 ΔT (° C.) 95 101 114 121 107 111 115 104 103 46 CompositionExamples Weight % 194 195 196 197 SiO2 59.00 58.70 58.19 59.00 Al2O312.00 11.90 11.84 12.00 CaO 22.50 22.40 21.33 22.50 MgO 3.40 3.40 2.823.40 TiO2 1.00 1.00 1.86 1.50 ZnO 1.00 1.50 2.28 0.50 Na2O 0.90 0.901.18 0.90 K2O 0.16 Fe2O3 0.20 0.20 0.24 0.20 SiO2/RO 2.28 2.28 2.24 2.28T_(FORM) (° C.) 1234 1231 1212 1230 (NIST 710A) T_(LIQ) (° C.) 1175 11811159 1183 ΔT (° C.) 69 50 53 37

[0040] TABLE F TYPE III-4 GLASS Composition Examples Weight % 198 199200 201 202 203 204 205 206 207 SiO2 58.00 57.90 57.80 58.15 58.25 58.0058.10 58.30 58.20 58.10 Al2O3 13.43 13.43 13.43 13.33 13.33 13.63 13.6313.03 13.03 13.03 CaO 23.44 23.54 23.64 23.39 23.29 23.24 23.14 23.5423.64 23.74 MgO 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 TiO20.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 B2O3 1.00 1.00 1.001.00 1.00 1.00 1.00 1.00 1.00 1.00 Na2O K2O Li2O 0.90 0.90 0.90 0.900.90 0.90 0.90 0.90 0.90 0.90 Fe2O3 0.23 0.23 0.23 0.23 0.23 0.23 0.230.23 0.23 0.23 SiO2/RO 2.24 2.22 2.21 2.25 2.26 2.25 2.27 2.24 2.23 2.21T_(FORM) (° C.) 1202 1203 1197 1203 1202 1207 1212 1200 1201 1194T_(LIQ) (° C.) 1139 1137 1139 1136 1145 1144 1146 1132 1137 1135 ΔT (°C.) 63 66 58 67 57 63 66 68 64 59 Composition Examples Weight % 208*209* 210* 211 212 213 214 215 216 217 SiO2 58.74 58.64 58.64 58.75 58.0057.80 57.60 57.60 57.60 57.60 Al2O3 13.05 13.15 12.95 12.93 13.03 13.2313.23 13.23 13.23 13.03 CaO 22.97 22.97 22.87 22.93 23.84 23.84 23.8423.84 23.84 24.04 MgO 2.36 2.36 2.36 2.36 2.50 2.50 2.50 2.50 2.50 2.50TiO2 0.49 0.49 0.49 0.50 0.50 0.50 0.50 0.50 0.50 0.50 B2O3 1.00 1.001.00 1.20 1.00 1.00 1.20 1.20 1.20 1.20 Na2O 0.04 0.10 0.20 0.20 K2O0.09 0.09 0.09 0.10 Li2O 0.91 0.91 0.91 0.90 0.90 0.90 0.90 0.80 0.700.70 Fe2O3 0.29 0.29 0.29 0.29 0.23 0.23 0.23 0.23 0.23 0.23 SiO2/RO2.32 2.32 2.32 2.32 2.20 2.19 2.19 2.19 2.19 2.17 T_(FORM) (° C.) 12101209 1204 1210 1198 1201 1200 1196 1208 1201 T_(LIQ) (° C.) 1145 11511142 1127 1138 1126 1125 1133 1135 1145 ΔT (° C.) 65 58 62 83 60 75 7563 73 56 Composition Examples Weight % 218 219 220 221 222 223 224 225226 227 SiO2 58.50 58.40 58.30 58.40 58.15 58.25 58.70 58.00 57.60 58.00Al2O3 12.76 12.76 13.03 13.03 13.33 13.33 12.75 13.03 13.03 13.03 CaO23.61 23.71 23.54 23.44 23.39 23.29 23.50 23.84 24.04 23.84 MgO 2.502.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 TiO2 0.50 0.50 0.50 0.500.50 0.50 0.50 0.50 0.50 0.50 B2O3 1.00 1.00 1.00 1.00 1.00 1.00 0.601.00 1.20 1.00 Na2O 0.60 K2O Li2O 0.90 0.90 0.90 0.90 0.90 0.90 0.600.90 0.90 0.90 Fe2O3 0.23 0.23 0.23 0.23 0.25 0.25 0.25 0.23 0.23 0.23SiO2/RO 2.24 2.23 2.24 2.25 2.25 2.26 2.26 2.20 2.17 2.20 T_(FORM) (°C.) 1202 1203 1201 1208 1197 1200 1216 1202 1194 1192 T_(LIQ) (° C.)1141 1145 1138 1137 1130 1134 1160 1137 1142 1137 ΔT (° C.) 61 58 63 7167 66 56 65 52 55 Composition Examples Weight % 228 229 230 231 232 233234 235 236 237 SiO2 58.61 58.61 58.00 57.90 58.11 58.40 58.40 58.5058.60 58.00 Al2O3 12.16 12.16 13.23 13.23 13.36 13.36 13.03 13.03 13.0313.63 CaO 23.50 23.50 23.64 23.74 23.40 23.11 23.44 23.34 23.24 23.24MgO 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 TiO2 1.10 1.100.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 B2O3 1.00 1.00 1.00 1.00 1.001.00 1.00 1.00 1.00 1.00 Na2O 0.45 K2O Li2O 0.90 0.45 0.90 0.90 0.900.90 0.90 0.90 0.90 0.90 Fe2O3 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.230.23 0.23 SiO2/RO 2.25 2.25 2.22 2.21 2.24 2.28 2.25 2.26 2.28 2.25T_(FORM) (° C.) 1201 1227 1201 1195 1196 1204 1201 1204 1204 1206T_(LIQ) (° C.) 1142 1159 1135 1137 1133 1133 1136 1133 1135 1136 ΔT (°C.) 59 68 66 58 63 71 65 71 69 70 Composition Examples Weight % 238 239240 241 242 243 244 245 246 247 SiO2 58.10 58.10 58.70 58.70 58.70 58.6158.40 58.80 58.30 57.60 Al2O3 13.23 13.43 12.75 12.35 12.35 12.16 12.7612.46 13.03 13.03 CaO 23.54 23.34 23.50 23.50 23.50 23.50 23.71 23.6123.54 24.04 MgO 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 TiO20.50 0.50 0.50 0.50 0.50 1.10 0.50 0.50 0.50 0.50 B2O3 1.00 1.00 0.601.00 1.00 1.00 1.00 1.00 1.00 1.20 Na2O 0.30 0.60 0.30 0.10 K2O Li2O0.90 0.90 0.90 0.60 0.90 0.90 0.90 0.90 0.90 0.80 Fe2O3 0.23 0.23 0.250.25 0.25 0.23 0.23 0.23 0.23 0.23 SiO2/RO 2.23 2.25 2.26 2.26 2.26 2.252.23 2.25 2.24 2.17 T_(FORM) (° C.) 1199 1204 1204 1207 1202 1194 11941195 1195 1196 T_(LIQ) (° C.) 1133 1134 1153 1157 1149 1141 1144 11451140 1145 ΔT (° C.) 63 70 51 50 53 53 50 50 55 51 Composition ExamplesWeight % 248 249 250 251 252 253 254 255 256 257 SiO2 58.50 58.11 58.9158.11 58.30 58.20 58.10 58.70 58.70 58.11 Al2O3 12.76 13.36 12.16 13.3613.03 13.03 13.03 13.35 13.35 13.36 CaO 23.61 23.40 23.80 23.40 23.5423.64 23.74 23.50 23.50 23.40 MgO 2.50 2.50 2.50 2.50 2.50 2.50 2.502.50 2.50 2.50 TiO2 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50B2O3 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.30 0.60 1.00 Na2O K2O Li2O0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.60 0.90 Fe2O3 0.23 0.23 0.230.23 0.23 0.23 0.23 0.25 0.25 0.23 SiO2/RO 2.24 2.24 2.24 2.24 2.24 2.232.21 2.26 2.26 2.24 T_(FORM) (° C.) 1197 1229 1216 1213 1202 1202 12051207 1224 1212 T_(LIQ) (° C.) 1139 1155 1148 1142 1136 1136 1137 11441145 1135 ΔT (° C.) 58 133 123 126 120 119 122 114 142 139 CompositionExamples Weight % 258 259 260 261 262 263 264 265 266 267 SiO2 58.2058.70 59.53 59.61 59.11 59.11 59.16 59.21 57.80 59.11 Al2O3 13.23 12.3512.25 12.16 12.16 12.16 12.16 12.16 13.03 12.16 CaO 23.44 23.50 23.1723.50 23.00 23.00 23.20 23.40 24.04 23.50 MgO 2.50 2.50 2.52 2.50 2.502.50 2.25 2.00 2.50 2.00 TiO2 0.50 0.50 0.50 1.10 1.10 1.10 1.10 1.100.50 1.10 B2O3 1.00 1.00 1.00 0.45 1.00 1.00 1.00 1.00 1.00 1.00 Na2OK2O Li2O 0.90 1.20 0.80 0.45 0.90 0.90 0.90 0.90 0.90 0.90 Fe2O3 0.230.25 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 SiO2/RO 2.24 2.26 2.32 2.292.32 2.32 2.32 2.33 2.18 2.32 T_(FORM) (° C.) 1204 1187 1214 1230 12051216 1218 1213 1196 1209 T_(LIQ) (° C.) 1135 1147 1143 1155 1142 11431147 1153 1147 1153 ΔT (° C.) 124 40 71 75 63 73 71 60 49 56 CompositionExamples Weight % 268 269 270 271 272 273 274 275 276 277 SiO2 59.3659.31 59.36 59.41 59.11 59.16 59.21 59.16 59.11 59.01 Al2O3 12.41 12.5612.51 12.46 12.16 12.16 12.16 12.26 12.26 12.36 CaO 23.60 23.50 23.5023.50 23.00 23.20 23.40 23.45 23.50 23.50 MgO 2.00 2.00 2.00 2.00 2.502.25 2.00 2.50 2.50 2.50 TiO2 0.50 0.50 0.50 0.50 1.10 1.10 1.10 0.500.50 0.50 B2O3 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Na2OK2O Li2O 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 Fe2O3 0.230.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 SiO2/RO 2.32 2.33 2.33 2.332.32 2.32 2.33 2.28 2.27 2.27 T_(FORM) (° C.) 1216 1220 1220 1220 12161214 1220 1209 1210 1210 T_(LIQ) (° C.) 1153 1153 1158 1155 1144 11471158 1150 1152 1152 ΔT (° C.) 63 67 62 65 72 67 62 59 58 58 CompositionExamples Weight % 278 279 280 281 282 283 284 285 286 287 SiO2 58.9158.91 59.21 58.31 58.61 58.70 58.60 58.50 58.75 58.75 Al2O3 12.36 12.1612.16 12.16 12.76 12.46 12.46 12.46 12.93 12.93 CaO 23.60 23.80 23.5024.40 23.50 23.71 23.81 23.91 22.93 22.93 MgO 2.50 2.50 2.50 2.50 2.502.50 2.50 2.50 2.36 2.36 TiO2 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.500.50 0.50 B2O3 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.20 1.20 Na2O0.14 0.24 K2O 0.10 0.10 Li2O 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.900.80 0.70 Fe2O3 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.29 0.29SiO2/RO 2.26 2.28 2.28 2.17 2.25 2.24 2.23 2.22 2.32 2.32 T_(FORM) (°C.) 1196 1196 1201 1195 1183 1193 1192 1191 1211 1218 T_(LIQ) (° C.)1152 1156 1143 1151 1165 1152 1151 1152 1127 1129 ΔT (° C.) 44 40 58 4418 41 41 39 84 89 Composition Examples Weight % 288 289 290 291 292 293294 295 296 297 298 SiO2 58.50 58.70 58.70 58.10 58.70 58.91 59.11 59.3159.21 60.12 59.11 Al2O3 12.34 13.05 12.75 13.63 13.35 12.16 12.16 12.2612.26 13.00 12.16 CaO 23.70 23.50 23.50 23.14 23.50 23.80 23.50 22.3023.40 21.13 23.00 MgO 2.50 2.50 2.50 2.50 2.50 2.50 2.00 2.50 2.50 2.502.50 TiO2 0.50 0.50 0.50 0.50 0.50 0.50 1.10 0.50 0.50 1.10 1.10 B2O31.20 0.30 0.60 1.00 0.90 1.00 1.00 1.00 1.00 1.00 1.00 Na2O 0.45 K2O0.08 LiO2 0.90 .20 1.20 0.90 0.30 0.90 0.90 0.90 0.90 0.90 0.45 Fe2O30.28 0.25 0.25 0.23 0.25 0.23 0.23 0.23 0.23 0.25 0.23 SiO2/RO 2.23 2.262.26 2.27 2.26 2.24 2.32 2.39 2.29 2.54 2.32 T_(FORM) (° C.) 1195 11961195 1204 1239 1197 1215 1209 1210 1285 1243 T_(LIQ) (° C.) 1151 11471147 1115 1143 1155 1155 1148 1156 1189 1149 ΔT (° C.) 44 49 48 89 96 4260 61 54 96 94

[0041] The samples were experimental samples produced in a laboratory.The experimental samples were prepared from reagent grade oxides (e.g.,pure silica or calcia). The batch size for each example was 1000 grams.The individual batch ingredients were weighed out, combined and placedin a tightly sealed glass jar or plastic container. The sealed jar orcontainer was then placed in a paint shaker for 15 minutes or in aturbular mixer for 25 minutes to effectively mix the ingredients. Aportion of the batch was then place into a platinum crucible, filling nomore than ¾ of its volume. The crucible was then placed in a furnace andheated to 1427° C. (2600° F.) for 15 minutes. The remaining batch wasthen added to the hot crucible and heated to 1427° C. (2600° F.) for 15to 30 minutes. The furnace temperature was then raised to 1482° C.(2700° F.) and held there for 2 hours. The molten glass was then frittedin water and dried. The fritted samples were remelted at 1482° C. (2700°F.) and held there for 2 hours. The molten glass was then fritted againin water and dried. The forming temperature, i.e. the glass temperatureat a viscosity of 1000 poise, was determined by ASTM method C965-81, andthe liquidus temperature by ASTM method C829-81.

[0042] The weight percent of the constituents of the compositions shownin Tables A through F are based on the weight percent of eachconstituent in the batch. It is believed that the batch weight percentis generally about the same as the weight percent of the melted sample,except for glass batch materials that volatilize during melting, e.g.boron and fluorine. For boron, it is: believed that the weight percentof B₂O₃ in a laboratory sample will be 5 to 15 percent less than theweight percent of B₂O₃ in the batch composition, the precise lossdepending on the composition and melting conditions. For fluorine, It isbelieved that the weight percent of fluorine in a laboratory test samplewill be about 50 percent less than the weight percent of fluorine in thebatch composition, the precise loss depending on the composition andmelting conditions. It is further believed that glass fiber compositionsmade from commercial grade materials and melted under conventionaloperating conditions will have similar batch and melt weight percents asdiscussed above, with the precise loss depending, in part, on thefurnace operating temperature, through-put and quality of commercialbatch materials. The amount of born and fluorine reported in the tablestakes into consideration the expected loss of these materials andrepresents the expected amount of the material in the glass composition.

[0043] Determination of the log 3 forming temperature was based on theglass samples being compared against physical standards supplied by theNational Institute of Standards and Testing (NIST). In Tables A throughF, the reported log 3 forming temperature is based on comparison toeither NIST 710A or NIST 714, both of which are a soda lime silica glassstandard. It is expected that both standards will provide comparableresults since both are based on a soda lime silica standard. The T_(LIQ)is unaffected by the NIST standard. Unless otherwise stated, the log 3forming temperatures reported herein are based on the NIST 714 standard.

[0044] In the present invention, the compositional variables of interestare the weight percent SiO₂ and weight percent RO, and the relationshipof interest is the ratio of SiO₂ to RO, i.e. SiO₂/RO. The meltproperties of interest are the forming temperature and the liquidustemperature since one goal in the present invention is to provide a lowboron glass composition having a lowered forming temperature and adesired ΔT so that the composition can be processed at a loweredtemperature while reducing the possibility of devitrification of themolten glass in the bushing area during a glass fiber forming operation.Without limiting the present invention, in one nonlimiting embodiment,the glass composition has a ΔT of at least 50° C. (90° F.), e.g. atleast 55° C. (100° F.). In other nonlimiting embodiments, the glasscomposition has a ΔT of 50 to 100° C. (90 to 180° F.), or 50 to 83° C.(90 to 150° F.), or 50 to 72° C. (90 to 130° F.).

[0045] Referring to FIGS. 1 through 6, the relationship between theSiO₂/RO ratio is plotted against both the forming temperature andliquidus temperature of the sample. The most suitable trendlines for thetemperatures are based on a second order regression analysis protocol,and in particular are 2nd order polynomial curves generated usingMicrosoft® Excel 97 SR-2(f). By inference, both trendlines also show theresulting change of the ΔT between liquidus and forming temperatures.

[0046] In viewing FIGS. 1 through 6, it can be seen that as the SiO₂/ROratio decreases, the forming temperature generally decreases, while thetrend in the liquidus temperature differs depending on the glass type.In addition, it can be seen that as the SiO₂/RO ratio decreases, ΔT alsodecreases. As a result, the SiO₂/RO ratio can be used to reduce theforming temperature of a glass fiber forming composition while providinga desired ΔT. More particularly, in the present invention where ΔT is atleast 50° C., a composition having a ΔT of 50° C. is indicative of acomposition having a combination of materials and amounts that providesa minimum permissible forming temperature, i.e. the lowest formingtemperature for the particular combination of constituents that stillmaintains the desired range between the forming and liquidustemperatures. From this, it can be inferred that the narrower the ΔTrange, the closer the glass forming temperature is to having the minimumpermissible forming temperature for that particular combination ofconstituents. It can also be inferred that the further the ΔT of a glasscomposition is from the minimum permissible ΔT, the greater theopportunity to modify the glass composition in a manner that reducesT_(FORM) while maintaining a ΔT no less than the minimum permissible ΔT.To this end, the SiO₂/RO ratio can be manipulated by changing the amountof SiO₂ and/or RO to produce a glass composition having a ΔT as close aspossible to the minimum desired ΔT. It should be appreciated that if theSiO₂/RO ratio drops too low, ΔT can drop to an unacceptable level.Although not required, in one nonlimiting embodiment of the presentinvention, SiO₂/RO is no greater that 2.35. In other nonlimitingembodiments, SiO₂/RO is no greater than 2.30, or no greater than 2.25,or no greater than 2.20. In still another nonlimiting embodiment of theinvention, SiO₂/RO ranges from 1.9 to 2.3, e.g. 2.05 to 2.29.

[0047] Although Tables A through F and corresponding FIGS. 1 through 6illustrate how the ratio of the weight percent of SiO₂ to RO effects themelt properties of the glass, and in particular the liquidustemperature, forming temperature and ΔT, additional glass samplecompositions as well as additional relationships between the glassconstituents, such as for example the difference in the amount of SiO₂and RO (i.e. SiO₂ wt %-RO wt %), the weight percent of Al₂O₃, the ratioof SiO₂ to Al₂O₃, and the ratio of RO to Al₂O₃, as they relate toliquidus and forming temperatures and ΔT, are disclosed in U.S.Provisional Application No. 60/230474, which is incorporated herein byreference.

[0048] It is known that pure silica is the highest melting glass former.A pure silica melt does not have a well defined melting point, butgradually solidifies and forms a glass as it cools to room temperatureand its viscosity drops from greater than log 4 (10,000) poise at 2500°C. (1371° F.). Pure calcia, magnesia and alumina melts are known to havevery low viscosities of 0.5-2 poise at their respective melting points.These materials do not solidify into a glass but rather crystallizeinstantly at their sharply defined melting point. In a typicalquaternary SiO₂—Al₂O₃—CaO—MgO glass composition with 60% SiO₂ and 21%CaO, each oxide contributes its unique characteristics toward itsbalance of melt properties.

[0049] Based on these material properties, it can be inferred that asSiO₂, which is the largest oxide component of the glass composition interms of weight percent, is reduced in a given composition of this type,the melt viscosity and the resulting log 3 forming temperature drops. IfCaO, which is the second largest component of the glass composition interms of weight percent, is increased in such a composition, the effectof RO (CaO+MgO) on the glass properties will be twofold. Morespecifically, it will not only increase the fluidity of the resultingmelt (i.e. decrease its viscosity) but it will also increase thecrystallizability of the resulting melt (i.e. increase its liquidustemperature), and therefore reduce the ΔT.

[0050] As a result, although not required, in one nonlimiting embodimentof the present invention, the glass compositions have (1) the lowestSiO₂ content that will yield the lowest log 3 forming temperatures, incombination with (2) the ratio of SiO₂ to RO (RO=CaO+MgO) that yieldsthe process-required ΔT, which in the present invention is at least 50°C.

[0051] Based on the above and although not required, in one nonlimitingembodiment of the present invention, the silica, level is kept low, i.e.no greater than 59 wt % SiO₂, in order to promote a lower log 3 formingtemperature. In other nonlimiting embodiments of the present invention,the glass compositions have no greater than 58 wt % SiO₂, or no greaterthan 57 wt % SiO₂.

[0052] Table G summarizes features of selected low boron glasscompositions disclosed in Tables A through F that have (i) a T_(FORM) ofno greater than 1240° C. (2264° F.), (ii) a ΔT in the range of 50-83° C.(90-150° F.) and (iii) no greater than 59 wt % SiO₂. It has been foundthat a forming temperature of greater than 1240° C. can accelerate theprecious metal loss in the glass fiber forming bushings. In othernonlimiting embodiments of the present invention, the formingtemperature is no greater than 1230° C., or no greater than 1220° C., orno greater than 1210° C., or no greater than 1200° C.

[0053] For comparison purposes, Table G also includes similar featuresof selected Type I-1 and I-2 glasses, two commercial boron containingE-glass compositions, and two commercial ADVANTEX glass compositions. Itis noted that none of these specific examples meets the selectioncriteria for the glasses of the present invention presented in Table G.TABLE G Composition % SiO₂ SiO₂/RO T_(FORM) (° C.) T_(LIQ) (° C.) ΔT (°C.) commercial glass 1¹ 55.2 2.31 1207 1069 138 (5.1 wt % B₂O₃)commercial glass 2¹ 53.1 2.32 1172 1077 95 (6.1 wt % B₂O₃) Type I-1glass (no boron) from Patent '106 59 2.27 1249² 1149 100 from Patent'144 - Ex. 1 60.18 2.46 1255² 1180 75 from Patent '329 59.05-60.082.18-2.43 1248-1289² 1169-1219 56-96 commercial ADVANTEX 59.36 2.26 12681180 88 glass sample 1³ commercial ADVANTEX 60.17 2.28 1266 1189 77glass sample 2³ Type I-2 glass from Patent '144 - Ex. 2 60.82 2.53 1262²1180 82 (1.8 wt % B₂O₃) Selection criteria ≦59 ≦1240 50-83 Type II-I (noboron) 57.45-58.05 2.13-2.21 1232-1240 1164-1167 66-74 Type II-2(w/B₂O₃) 55.4-58.55 2.03-2.28 1202-1240 1127-1178 55-83 Type III-1 (noboron) 57.65-58.96 2.16-2.26 1205-1237 1146-1172 52-69 Type III-2 (noboron) 57.35-58.30 2.18-2.29 1195-1213 1136-1157 54-71 Type III-3 (noboron) 58.19-59.00 2.24-2.28 1212-1234 1159-1181 50-69 Type III-4(w/B₂O₃) 57.60-58.80 2.17-2.32 1192-1227 1125-1160 50-83

[0054] Referring to Table G, it can be seen that the selected boron-freeType II-1, III-1, III-2 and III-3 glasses generally have less SiO₂, alower SiO₂/RO ratio, a lower forming temperature, and a narrower ΔTrange than the sample boron-free Type I-1 glasses. Similarly, theselected boron-containing Type II-2 and III-4 glasses generally haveless SiO₂, a lower SiO₂/RO ratio, a lower forming temperature, and anarrower ΔT range than the sample boron-containing Type I-2 glasses.Furthermore, the selected Type II and III glasses generally have ahigher SiO₂ content, a lower SiO₂/RO ratio, and a narrower ΔT range thanthe two commercial, high boron content samples.

[0055] Tables H, I, J and K illustrate additional glass compositionsaccording to the present invention. TABLE H Composition Examples Weight% 299 300 301 302 303 304 305 306 307 308 309 SiO2 56.25 56.45 56.7556.50 56.75 57.5 56.75 57.75 57.75 57.75 55.40 Al2O3 13.2 13.20 13.2013.20 13.20 12.2 13.2 12.2 12.2 12.2 13.6 CaO 24.25 24.25 23.95 24.0023.75 24 23.95 23.75 23.75 23.95 24.5 MgO 2.55 2.55 2.55 2.55 2.55 2.552.55 2.55 2.55 2.55 2.95 TiO2 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.101.10 1.10 1.10 Na2O 0.9 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.900.45 K2O 0.45 Fe2O3 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.250.25 B2O3 1.30 1.30 1.30 1.30 1.40 1.30 1.20 1.40 1.30 1.40 1.30 SiO2/RO2.10 2.11 2.14 2.13 2.16 2.17 2.14 2.20 2.20 2.18 2.02 T_(FORM) (° C.)1210 1214 1215 1215 1215 1216 1216 1217 1217 1218 1210 T_(LIQ) (° C.)1154 1159 1154 1154 1160 1152 1147 1151 1147 1155 1157 ΔT (° C.) 56 5561 61 55 64 69 66 70 63 53 Composition Examples Weight % 310 311 312 313314 315 316 317 318 319 320 SiO2 55.40 56.05 55.85 56.00 56.60 56.5056.10 56.50 55.95 56.50 56.45 Al2O3 13.60 13.10 13.38 13.37 13.25 13.4513.38 13.45 13.95 13.49 13.48 CaO 24.50 24.55 24.67 24.53 24.60 24.5024.42 24.50 24.55 24.46 24.52 MgO 2.95 2.75 2.55 2.55 2.55 2.55 2.552.55 2.55 2.55 2.55 TiO2 1.10 1.10 1.10 1.10 0.55 0.55 0.55 0.55 0.550.55 0.55 Na2O 0.45 0.45 0.45 0.45 0.90 0.90 0.90 0.90 0.90 0.90 0.90K2O 0.45 0.45 0.45 0.45 Fe2O3 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.250.25 0.25 0.25 B2O3 1.30 1.30 1.30 1.30 1.30 1.30 1.30 1.30 1.30 1.301.30 SiO2/RO 2.02 2.05 2.05 2.07 2.09 2.09 2.08 2.09 2.07 2.09 2.09T_(FORM) (° C.) 1211 1218 1220 1221 1211 1212 1215 1215 1216 1218 1219T_(LIQ) (° C.) 1151 1156 1148 1157 1153 1158 1150 1157 1162 1161 1158 ΔT(° C.) 60 62 72 64 58 54 65 58 54 57 61

[0056] TABLE I Composition Examples Weight % 312 322 323 324 325 326 327328 329 330 331 332 SiO2 55.50 55.25 55.00 55.75 55.50 55.25 54.20 54.5054.12 55.00 54.50 54.70 Al2O3 13.20 13.20 13.20 13.30 13.30 13.30 13.3513.25 13.30 13.25 13.25 13.20 CaO 23.50 23.75 24.00 23.70 23.95 24.2024.55 24.55 24.55 2425 24.55 24.50 MgO 2.55 2.55 2.55 2.55 2.55 2.552.55 2.55 3.00 2.55 2.67 2.55 TiO2 1.10 1.10 1.10 0.55 0.55 0.55 0.550.55 0.55 0.55 0.55 0.55 Na2O 0.90 0.90 0.90 0.90 0.90 0.90 0.45 0.450.45 0.45 0.45 0.45 K2O 0.55 0.55 0.55 0.55 0.55 0.55 B2O3 3.00 3.003.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 Fe2O3 0.250 0.2500.250 0.250 0.250 0.250 0.28 0.28 0.28 0.28 0.28 0.28 F 0.20 0.20 0.100.10 0.10 0.10 SrO 0.12 0.12 0.10 0.12 0.10 0.12 SiO2/RO 2.13 2.10 2.072.12 2.09 2.07 1.99 2.01 1.96 2.05 2.00 2.02 T_(FORM) (° C.) 1193 11981201 1201 1200 1198 1190 1194 1196 1197 1201 1201 T_(LIQ) (° C.) 11291122 1127 1127 1129 1128 1120 1124 1132 1124 1131 1119 ΔT (° C.) 64 7674 74 71 70 70 70 64 73 70 82

[0057] TABLE J Composition Examples Weight % 333 334 335 336 SiO2 53.0553.50 53.00 53.00 AL2O3 14.01 14.00 13.50 13.10 CaO 24.28 24.00 24.0024.00 MgO 1.00 1.50 2.50 2.90 TiO2 0.52 0.50 0.50 0.50 Na2O 0.53 0.900.90 0.90 Fe2O3 0.91 0.10 0.10 0.10 B2O3 5.10 4.94 4.93 5.02 K2O 0.100.37 0.37 0.37 F 0.52 0.50 0.50 0.50 SrO 0.13 0.13 0.13 0.13 Cr2O3 0.130.13 0.13 SiO2/RO 2.01 2.10 2.00 1.97 T_(FORM) (° C.) 1171 1177 11721167 T_(LIQ) (° C.) 1114 1122 1103 1110 ΔT (° C.) 57 57 69 57

[0058] TABLE K Composition Examples Weight % 337 338 339 SiO2 54.6056.75 57.85 Al2O3 13.35 13.20 12.45 CaO 24.55 23.95 24.05 MgO 2.55 2.552.55 TIO2 0.35 1.10 0.55 Na2O 0.15 0.60 0.60 Fe2O3 0.28 0.25 0.35 B2O33.00 1.40 1.30 K2O 0.55 F 0.20 SrO 0.12 Li2O 0.30 0.30 0.30 SiO2/RO 2.192.27 2.35 T_(FORM) (° C.) 1187 1206 1208 T_(LIQ) (° C.) 1133 1152 1154ΔT (° C.) 54 54 54

[0059] More particularly, the compositions in Table H are Type II-2glass compositions, i.e. low boron content glasses having 1.2 to 1.4 wt% B₂O₃, which have a low SiO₂ content ranging from 55.4 to 57.75 wt %, aSiO₂/RO ratio ranging from 2.02 to 2.20, a forming temperature rangingfrom 1210 to 1221° C. and a ΔT ranging from 54 to 72° C. Table Icompositions are also low boron Type II-2 compositions the include 3 wt% B₂O₃. These compositions have a low SiO₂ content ranging from 54.12 to55.75 wt %, a SiO₂/RO ratio ranging from 1.96 to 2.13, a formingtemperature ranging from 1193 to 1201° C. and a ΔT ranging from 64 to82° C. Table J includes additional Type II-2 compositions having a B₂O₃of around 5 wt %. Of particular note for the compositions in Table J arethe low SiO₂ contents (53.00 to 53.50 wt %), SiO₂/RO ratios (1.97 to2.10), forming temperatures (1167 to 1177° C.), and ΔT range (57 to 69°C.). Table K includes Type III-4 compositions that have a low SiO₂content ranging from 54.60 to 57.85 wt %, a SiO₂/RO ratio ranging from2.19 to 2.35, a forming temperature ranging from 1187 to 1208° C. and aΔT of 54° C.

[0060] Based on the above, in one nonlimiting embodiment of the presentinvention, the glass fiber composition comprises 52 to 62 percent byweight SiO₂, 0 to 2 percent by weight Na₂O, 16 to 25 percent by weightCaO, 8 to 16 percent by weight Al₂O₃, 0.05 to 0.80 percent by weightFe₂O₃, 0 to 2 percent by weight K₂O, 1 to 5 percent by weight MgO, 0 to5 percent by weight B₂O₃, 0 to 2 percent by weight TiO₂, and 0 to 1percent by weight F, wherein the glass composition has a log 3 formingtemperature of no greater than 1240° C. based on an NIST 714 referencestandard, a ΔT of at least 50° C., and a SiO₂/RO ratio of no greaterthan 2.35. In another nonlimiting embodiment, the SiO₂ content of theglass composition is no greater than 59 percent by weight, ΔT is in therange from 50 to 83° C., and the SiO₂/RO ratio is in the range from 1.9to 2.3, and further the log 3 forming temperature is no greater than1230° C. based on an NIST 714 reference standard. In still anothernonlimiting embodiment, the glass composition is boron-free.

[0061] In another nonlimiting embodiment of the present invention, theglass fiber composition comprises 53 to 59 percent by weight SiO₂, 0 to2 percent by weight Na₂O, 16 to 25 percent by weight CaO, 8 to 16percent by weight Al₂O₃, 0.05 to 0.80 percent by weight Fe₂O₃, 0 to 2percent by weight K₂O, 1 to 4 percent by weight MgO, 0 to 5 percent byweight B₂O₃, 0 to 2 percent by weight TiO₂, and 0 to 1 percent by weightF, wherein the glass composition has a log 3 forming temperature of nogreater than 1240° C. based on an NIST 714 reference standard, a ΔT inthe range of 50 to 100° C., and a SiO₂/RO ratio in the range of 1.9 to2.3.

[0062] In viewing the tables and figures, it should be appreciated thatmany of the sample compositions, although they have a ΔT greater thanthe minimum required ΔT for a particular process, they also have ahigher forming temperature than that of the compositions of the presentinvention due, in part, to their high silica levels and/or high SiO₂/ROratios. As a result, such compositions are more expensive to producecommercially, at least in terms of energy costs. Such compositionsinclude the Type I compositions discussed herein. In addition, thetables and figures contain many samples containing a ΔT less than theminimum desired ΔT of 50° C. (90° F.). These types of compositions canbe found across the compositional spectrum in each figure but especiallyat low silica and SiO₂/RO levels. Because of the narrower ΔT range, therisk of the molten glass solidifying in the bushing area during a glassfiber forming operation increases to an unacceptable level.

[0063] It will be appreciated by those skilled in the art that changescould be made to the embodiments described above without departing fromthe broad inventive concept thereof. It is understood, therefore, thatthis invention is not limited to the particular embodiments disclosed,but it is intended to cover modifications that are within the spirit andscope of the invention, as defined by the appended claims.

I claim:
 1. A glass fiber composition comprising: SiO₂   52 to 62percent by weight; Na₂O   0 to 2 percent by weight; CaO   16 to 25percent by weight; Al₂O₃   8 to 16 percent by weight; Fe₂O₃ 0.05 to 0.80percent by weight; K₂O   0 to 2 percent by weight; MgO   1 to 5 percentby weight; B₂O₃   0 to 5 percent by weight; TiO₂   0 to 2 percent byweight; and F   0 to 1 percent by weight;

wherein the glass composition has a log 3 forming temperature of nogreater than 1240° C. based on an NIST 714 reference standard, a ΔT ofat least 50° C., and a SiO₂/RO ratio of no greater than 2.35.
 2. Theglass fiber composition according to claim 1, wherein the SiO₂ contentis no greater than 59 percent by weight, ΔT is in the range from 50 to83° C., and the SiO₂/RO ratio is in the range from 1.9 to 2.3.
 3. Theglass fiber composition according to claim 2, wherein the SiO₂ contentis no greater than 58 percent by weight.
 4. The glass fiber compositionaccording to claim 2, wherein the log 3 forming temperature is nogreater than 1230° C. based on an NIST 714 reference standard.
 5. Theglass fiber composition according to claim 4, wherein the log 3 formingtemperature is no greater than 1210° C. based on an NIST 714 referencestandard.
 6. The glass fiber composition according to claim 2, whereinthe B₂O₃ content is no greater than 3 percent by weight.
 7. The glassfiber composition according to claim 6, wherein the B₂O₃ content is nogreater than 2 percent by weight.
 8. The glass fiber compositionaccording to claim 2, wherein the glass composition is boron-free. 9.The glass fiber composition according to claim 2, wherein the SiO₂/ROratio is no greater than 2.25.
 10. The glass fiber composition accordingto claim 9, wherein the SiO₂/RO ratio is no greater than 2.20.
 11. Theglass fiber composition according to claim 2, wherein the MgO content is1.7 to 2.9 percent by weight, the B₂O₃ content is no greater than 3percent by weight, and the TiO₂ content is no greater than 1.5 percentby weight.
 12. The glass fiber composition according to claim 11,wherein the glass composition is boron-free.
 13. The glass fibercomposition according to claim 2, wherein the glass composition furtherincludes at least one material selected from: Li₂O 0.05 to 1.5 percentby weight; ZnO 0.05 to 1.5 percent by weight; MnO 0.05 to 3 percent byweight; and MnO₂ 0.05 to 3 percent by weight.


14. The glass fiber composition according to claim 1, wherein the MgOcontent is 1 to 4 percent by weight, the B₂O₃ content is no greater than4 percent by weight, and the TiO₂ content is no greater than 2 percentby weight.
 15. The glass fiber composition according to claim 14,wherein the forming temperature is no greater than 1230° C. based on anNIST 714 reference standard.
 16. The glass fiber composition accordingto claim 14, wherein the SiO₂/RO ratio is no greater than 2.30.
 17. Theglass fiber composition according to claim 14, wherein ΔT is in therange from 50 to 83° C.
 18. The glass fiber composition according toclaim 1, wherein the forming temperature is no greater than 1230° C.based on an NIST 714 reference standard.
 19. The glass fiber compositionaccording to claim 18, wherein the forming temperature is no greaterthan 1220° C. based on an NIST 714 reference standard.
 20. The glassfiber composition according to claim 19, wherein the forming temperatureis no greater than 1210° C. based on an NIST 714 reference standard. 21.The glass fiber composition according to claim 1, wherein the SiO₂content is no greater than 59 percent by weight.
 22. The glass fibercomposition according to claim 21, wherein the SiO₂ content is nogreater than 58 percent by weight.
 23. The glass fiber compositionaccording to claim 1, wherein the TiO₂ content is no greater than 1.5percent by weight.
 24. The glass fiber composition according to claim 1,wherein the MgO content is 1 to 4 percent by weight.
 25. The glass fibercomposition according to claim 24, wherein the MgO content is 1.9 to2.65 percent by weight.
 26. The glass fiber composition according toclaim 1, wherein the B₂O₃ content is no greater than 4 percent byweight.
 27. The glass fiber composition according to claim 26, whereinthe B₂O₃ content is no greater than 2 percent by weight.
 28. The glassfiber composition according to claim 1, wherein the glass composition isboron-free.
 29. The glass fiber composition according to claim 1,wherein the glass composition is fluorine-free.
 30. The glass fibercomposition according to claim 1, wherein the SiO₂/RO ratio is nogreater than 2.30.
 31. The glass fiber composition according to claim30, wherein the SiO₂/RO ratio is no greater than 2.25.
 32. The glassfiber composition according to claim 31, wherein the SiO₂/RO ratio is nogreater than 2.20.
 33. The glass fiber composition according to claim 1,wherein the SiO₂/RO ratio is in the ranges from 1.9 to 2.30.
 34. Theglass fiber composition according to claim 35, wherein the SiO₂/RO ratiois in the ranges from 2.05 to 2.29.
 35. The glass fiber compositionaccording to claim 1, wherein ΔT is at least 55° C.
 36. The glass fibercomposition according to claim 1, wherein ΔT is in the range from 50 to100° C.
 37. The glass fiber composition according to claim 36, whereinΔT is in the range from 50 to 83° C.
 38. The glass fiber compositionaccording to claim 1 wherein the glass composition further includes atleast one material selected from: Li₂O 0.05 to 1.5 percent by weight;ZnO 0.05 to 1.5 percent by weight; MnO 0.05 to 3 percent by weight; andMnO₂ 0.05 to 3 percent by weight.


39. A glass fiber composition comprising: SiO₂   53 to 59 percent byweight; Na₂O   0 to 2 percent by weight; CaO   16 to 25 percent byweight; Al₂O₃   8 to 16 percent by weight; Fe₂O₃ 0.05 to 0.80 percent byweight; K₂O   0 to 2 percent by weight; MgO   1 to 4 percent by weight;B₂O₃   0 to 5 percent by weight; TiO₂   0 to 2 percent by weight; and F  0 to 1 percent by weight; Li₂O   0 to 1.5 percent by weight; ZnO   0to 1.5 percent by weight; MnO   0 to 3 percent by weight; and MnO₂   0to 3 percent by weight.

wherein the glass composition has a log 3 forming temperature of nogreater than 1240° C. based on an NIST 714 reference standard, a ΔT inthe range from 50 to 100° C., and a SiO₂/RO ratio is in the range from1.9 to 2.30.
 40. The glass fiber composition according to claim 39,wherein the glass composition has a ΔT in the range from 50 to 83° C.41. The glass fiber composition according to claim 39, wherein SiO₂/ROratio is no greater than 2.25.
 42. The glass fiber composition accordingto claim 39, wherein the log 3 forming temperature is no greater than1230° C. based on an NIST 714 reference standard.